Set startUpTime of Proxy

Author: LEDfan

src/main/java/eu/openanalytics/containerproxy/backend/AbstractContainerBackend.java

@@ -142,7 +142,8 @@ public void startProxy(Proxy proxy) throws ContainerProxyException {
 			stopProxy(proxy);
 			throw new ContainerProxyException("Container did not respond in time");
 		}
-		
+
+		proxy.setStartupTimestamp(System.currentTimeMillis());
 		proxy.setStatus(ProxyStatus.Up);
 	}